In various applications involving complex electrical and/or optical equipment, such as large computers and telephone exchanges, there exists a need for interconnecting a large number of signal carrying "lines", e.g., metal wires or optical fibers, and for processing the signals being conveyed. Also, flexibility is required for readily changing the system architecture in response to changing needs, e.g., relocation and/or changing service requirements of subscribers to a telephone system.
For accommodating these requirements, "card racks" (or "card cages") have evolved. Such card racks comprise a relatively large enclosure including racks or shelves for removably receiving "cards", i.e., printed circuit boards known as "circuit packs". Each circuit pack includes a plurality of signal processing components mounted on a rigid plate including conductive paths for interconnecting the components to one another and to various connectors also mounted on the rigid plate. The circuit packs are removably mounted, generally in side-by-side relationship, within the card rack by sliding edges of the rigid plates along grooves within support walls of the card rack. Connectors at the leading ends of the rigid plates mate with connectors fixedly mounted within the card rack.
For ease of insertion and removal of the circuit packs (for changing the system configuration), the circuit packs are fully accessible at a front surface of the card rack. Signal carrying lines disposed within cables are connected to various ones of the circuit packs at the card rack front surface, and the cables project forwardly from the card rack front surface before being led away through various cable conduits or channels.
A problem, and particularly in large rooms containing many side-by-side disposed card racks, is that the forwardly projecting cables at the front surfaces of the card racks are subject to being snared by or entangled with traffic passing in front of the card racks, e.g., attendants and equipment carrying carts. One common solution is to provide hinged front doors for enclosing both the front surfaces of the card racks and the portions of the cables projecting immediately forwardly thereof.
The use of hinged front doors, however, presents a new set of problems in that the doors add complexity and expense to the card racks; add delays in obtaining access to the card racks; and inevitably provide dangerous obstacles to traffic passing in front of the card racks.